Matrix and method of making same

ABSTRACT

Disclosed is an improved assembly or matrix in which a plurality of open-ended, glass-ceramic tubes are disposed in axially parallel relation. The tubes are rigidified into a matrix structure, with the tubes being integrally bound to each other at their tube contact areas. Additional glass-ceramic material at and just below the surface of the matrix structure and arranged in a predetermined pattern across the open-ended face of the matrix integrally binds together the surfaces of the tubes facing the interstices between the tubes. That portion of the pattern overlying the open ends of the tubes fills the tube openings. The additional glass-ceramic material thus provides a wear resistant, matrix-reinforcing surface, a control of the porosity of the matrix structure, and a control of the flow pattern through the matrix. The invention also comprehends the method of reinforcing a matrix of this type by interposing a finely divided, thermally crystallizable frit or other forms of low expansion crystallizable glass between and in the open ends of individual, matrix-defining glass tubes in a predetermined pattern across the open-ended face of a matrix structure and thermally processing the frit or other form of crystallizable glass to convert the frit or other material to low-expansion, glass-ceramic material of substantially the same thermal expansion characteristics as the matrix structure and to fusion bond the frit or other material to the matrix structure.

United States Patent [1 1 Sayers 1451 Nov. 13, 1973 MATRIX AND METHOD OFMAKING SAME [75] Inventor: James A. Sayers, Toledo, Ohio [73] Assignee:Owens-Illinois, Inc., Toledo, Ohio 22 Filed: Aug. 16, 1971 [21] Appl.No.: 171,881

[52] US. Cl. 165/10, 65/33, 65/DIG. 7, 161/68, 161/69 [51] Int. Cl. F28d19/04 [58] Field of Search 165/10; 65/DIG. 7, 65/33; 161/68, 69

[56] References Cited UNITED STATES PATENTS 3,372,735 3/1968 Meijer165/10 X 3,392,776 7/1968 Topouzian 165/10 X 3,482,622 12/1969 Bracken,Jr. et a1. 165/10 X 3,556,636 1/l97l Roberts et al. 65/D1G. 7

3,549,468 12/1970 Messineo et a1... 161/68 3,582,301 6/1971 Andrysiab eta1 65/33 3,607,185 9/1971 Andrysiab 65/D1G. 7

Primary Examiner-Albert W. Davis, Jr. Attorney-E. J. Holler et al.

57 ABSTRACT Disclosed is an improved assembly or matrix in which aplurality of open-ended, glass-ceramic tubes are disposed in axiallyparallel relation. The tubes are rigidified into a matrix structure,with the tubes being integrally bound to each other at their tubecontact areas. Additional glass-ceramic material at and just below thesurface of the matrix structure and arranged in a predetermined patternacross the open-ended face of the matrix integrally binds together thesurfaces of the tubes facing the interstices between the tubes. Thatportion of the pattern overlying the open ends of the tubes fills thetube openings. The additional glassceramic material thus provides a wearresistant, matrix-reinforcing surface, a control of the porosity of thematrix structure, and a control of the flow pattern through the matrix.The invention also comprehends the method of reinforcing a matrix ofthis type by interposing a finely divided, thermally crystallizable fritor other forms of low expansion crystallizable glass between and in theopen ends of individual, matrixdefining glass tubes in a predeterminedpattern across the open-ended face of a matrix structure and thermallyprocessing the frit or other form of crystallizable glass to convert thefrit or other material to low-' expansion,"glass-ceramic material ofsubstantially the same thermal expansion characteristics as the'matrixstructure and to fusion bond the frit or other material to the matrixstructure.

9 Claims, 16 Drawing Figures l/III I II I I 1 1 1 Patented Nov. 13, 19734' Sheets-Sheet 1 FICJB FICiZ lO-w . FIG. 4

ZOJ INVENTOR Patented Nov. 13,1973 3,771,592

4 Sheets-Sheet 2 INVENTOR JAMES A. .SAYERS Patented Nov. 13, 1973 4Sheets-Sheet 3 $IGU11 INVENTOR JAMES -A. SAYERS ATT RNEY Patented Nov.13, 1973 3,771,592

4 Sheets-Sheet 4 FIQIE FE B TIC514 FIG15 INVENTOR JAMES A. SAYERS T1616u f} AT ORNEY MATRIX AND METHOD OF MAKING SAME BACKGROUND OF THEINVENTION This invention constitutes an improvement over the structuresand methods disclosed in the application of Y. K. Pei, Ser. No. 30,859,filed in the U.S. Patent Office on Apr. 22, 1970, and in the applicationof Marion I. Gray, Jr., both assigned to the assignee of the presentinvention.

In the above-noted application of Pei, there is disclosed an assembly ormatrix of integrally fused tubes useful as a compact regenerative heatexchanger, buoyancy material, sound absorption material, heat insulationmaterial, and the like. The advantages of this type of structure and therequirements for each of the structures of this type, particularly aregenerator structure, are set forth fully in the Pei application andneed not be repeated here.

In the Pei application, there is disclosed a regenerator structure whichconsists of a plurality of individual, axially parallel, open endedglass-ceramic tubes which are thermally bonded to one another andintegrated into an overall regenerator structure. Gas flow through theregenerator occurs through the individual tubes, one open end of eachtube forming an inlet and the other open end of the tube forming theoutlet. In a typical thermal regenerator installation, one or both facesof the regenerator is contacted by a seal bar. The regenerator matrix isrotated relative to the seal bar which is urged against the regeneratorend surface under an appreciable axial load. Because of matrix endface-seal bar contact under the sealing load, some abrasive wearing ofthe matrix end face may well occur over an extended service period,particularly since the matrix end face is defined by the open ends ofthe individual tubes. Additionally, the strength of the matrix and itsability to withstand axially or radially applied loads in operation isdependent upon the degree of integral bonding between adjacent tubes.While matrices made in accordance with the disclosure of the Peiapplication are capable of functioning as regenerators or otherstructures disclosed therein, any increase in the resistance of thematrix end faces to wear and any increase in the strength of the matrixitself was welcomed.

In the Gray application, there is disclosed a matrix structure similarto that disclosed in the Pei application, but having the dualcharacteristics of increased structural strength and increased abrasionresistance at the open end faces of a matrix. That dual improvement wasaccomplished by reinforcing the matrix with a low expansion thermallycrystallizable glass which is interposed in the interstices between thetubes. The interposed material serves to bond the tubes to one anotherand to provide a wear resistant reinforcement at the seal-engagin gsurfaces of the matrix by insuring that the tube walls at the open endsthereof are supported by the interposed material or by an adjacent tubewall.

While matrices made in accordance with the disclosure of the Grayapplication function very well as regenerators or other structuresdisclosed therein, it is desirable to increase the resistance of thematrix end faces to wear with a less expensive and complex process, andwhile so reinforcing the matrix end face be able to control the porosityof and flow patterns through the matrix.

SUMMARY OF Tl-IE INVENTION The present invention provides a matrixsimilar to that disclosed in the Pei and Gray applications, but havingthe characteristics of increased abrasion resistance at the open endfaces of a matrix along with porosity and flow pattern control.

These improvements are accomplished by reinforcing the matrix face witha low expansion thermally crystallizable glass which is selectively laidin a desired pattern across the face of the matrix. This depositedmaterial serves to bond the tubes ends to one another and to fill thetube ends under the deposited material to provide a wear-resistant,tube-reinforcing surface or surfaces for the seal-engaging surfaces ofthe matrix.

In a preferred embodiments of the method taught herein, a glass-ceramicmatrix of the type disclosed in the Pei application is reinforced bydepositing a finely divided, thermally crystallizable frit in apredetermined, open network pattern in the open ends of and betweenindividual, matrix-defining glass tubes covered by the pattern after thethermal conversion of the tubes to a glass-ceramic. Subsequently, thethermally crystallizable frit is thermally processed through successivenucleating and crystallizing steps to convert the frit to low expansionglass-ceramic material having substantially the same thermal expansioncharacteristics as that of the tubes defining the matrix. During thissubsequent thermal processing, the thermal sintering of the fritintegrates the tube-frit pattern assembly into a single mass. After thenucleation and crystallizing steps have been carried out, the faces ofthe matrix may be ground to provide a seal-engaging surface which mateswith a particular seal configuration. The sintered frit is interposedbetween and in the ends of the tubes covered by the pattern, and servesto provide an additional, wear-resistant surface for the matrixassembly.

It is, therefore, an important object of this invention to provide amatrix structure or similar assembly of improved strength andwear-resistance properties by incorporating into the surface of thematrix a pattern of glass-ceramic material having thermal expansioncharacteristics compatible with that of the glass-ceramic tubes formingthe primary matrix structure.

Another important object of this invention is the provision of a methodof making a reinforced glassceramic matrix by the steps of assembling aplurality of individual, closed-end tubes of thermally crystallizableglass-ceramic material, thermally processing the tubes to convert thetubes to a low expansion glass-ceramic integral matrix structure,selectively laying down thermally crystallizable ceramic material in anopen network pattern on an open-ended face of the matrix structure, andthermally processing the selectively disposed ceramic material of thepattern to convert the selectively disposed ceramic material to aceramic'material fusion bonded to the matrix structure and havingsubstantially the same thermal expansion characteristics as the matrixstructure.

Yet another, and no less important, object of this invention is theprovision of a method for reinforcing a matrix structure formed from aplurality of tightly packed individually axially elongated tubesarranged with their axes parallel and the tube walls fusion bonded toeach other to form an integral mass by inter posing between the tubesand in the open ends thereof a thermally crystallizable frit distributedin an open network pattern across the open-ended face of the matrix, andsuccessively nucleating and crystallizing to convert the frit to aceramic having substantially the same thermal expansion characteristicsas the matrix and fusion bonded in the open ends of and between tubescovered by the pattern.

Other objects, features and advantages will become apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a perspective view of a jig assembly utilized in making anembodiment of the structure of the invention and showing a partialpacking of tubes within the structure mounted on the assembly;

FIG. 2 is a side view of a glass tube used in making the structure ofthis invention;

FIG. 3 is an enlarged cross-sectional view of the glass tube taken alonglines III-III of FIG. 2;

FIG. 4 is a partial cross-sectional view of the structure of FIG. Iplaced within an assembly prior to heat treatment;

FIG. 5 is a sectional view of a portion of the bundle of tubes of theinvention, greatly enlarged, showing the arrangement of the glass tubesprior to being expanded by heat treatment;

FIG. 6 is a sectional view of a portion of the bundle of tubes of thestructure of the invention, greatly enlarged, showing the arrangement ofthe glass tubes after they have been expanded and crystallized by heattreatment;

FIG. 7 is an enlarged view of a portion of assembled tubes from abundle, the tubes being coated with a thermally crystallizable frit;

FIG. 8 is a cross-sectional view of the tubes illustrated in FIG. 7, thesection being taken along lines VIII-VIII of FIG. 7;

FIG. 9 is a view of the tubes illustrated in FIG. 7 formed into an openend matrix structure;

FIG. 10 is a top plan view, greatly enlarged, of a portion of a matrixtaken from the apparatus of FIG. 4 showing application of reinforcingmaterial according to the teachings of this invention;

FIG. 1 l is a cross-sectional view of the matrix portion shown in FIG.10, the section being taken along lines XI-XI of FIG. 10; and

FIGS. 12, 13, 14, and 16 are plan views of matrix structures showingdiagrammatically aternative patterns of application of reinforcingmaterial in accordance with the method illustrated in FIGS. 10 and 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in the drawings, FIG.1, reference number 10 refers generally to an apparatus which issubstantially identical to that apparatus illustrated in FIG. 1 of theabove-identified application of Y. K. Pei

As illustrated in FIG. 1, a ceramic rim 10 is mounted on a jig 11comprising a face board 12 attached to a conventional vibrator 13. Threeclamping means 14 are I spaced about the edges of face board 12 andremovably secure the rim l0 thereto. Each of clamping means 14 comprisea stem portion 15 fastened to the face board, an arm portion 16 disposedat right angles to the stem portion 15 and provided with a fingerportion 17 in contact with the upper edge 18 of rim 10. Arm portions 16are held in engagement with the rim 10 and the stem portion 15 byfastening means 19 passing through arm portion 16 and secured to theface board 12.

A hub 20 may be also removably mounted on the face board 12 and disposedat the center of the rim. Fastener 21 passing through the hub 20 issecured to the face board 12 and maintains the hub in position on thejig. A plurality of hollow, thin-walled thermally crystallizable glasstubes 22 are then closely packed together with the rim in parallelrelationship as illustrated in FIG. 1, i.e., the tubes are parallel tothe inner wall 23 of the rim and the outer wall 24 of the hub and thelongitudinal axes of the tubes are essentially parallel.

Each of the glass tubes 22 shown in FIGS. 1, 2 and 3 have both ends 22'sealed, thus trapping air or another thermally expansible fluid mediumtherein. A tube 22 may have its ends sealed by simply passing the tubeend through a flame. Due to the very small size of the tube, the outerdiameter of which may, for example, be about 0.030 inches and the wallthickness may be about 0.001 to 0.003 inches, end scaling is readilyachieved. However, the method of sealing the tubes is not a part of thisinvention, and any of the known methods may be usd.

Because it is often desirable and important to have the glass tubes 22as closely packed as possible so that each tube is in contact with sixother tubes, as shown in FIG. 5, the jig 11 is provided with a vibratorl3 1 which, in turn, causes face board 12 and rim 10 to vibrate (bymeans not shown). This vibration is imparted to the plurality of glasstubes 22 and assists in more closely packing the tubes as they areplaced .on top of the tubes which have already been packed. It is to beunderstood that the rim 10 need not be manually packed, but can bepacked by other methods. In either event, the vibration imparted to theglass tubes should be sufficient to ensure the close, tight packing ofthe tubes within the rim, with each tube in contact with six othertubes.

The assembly 25 comprising the rim 10, hub 20 and the closely-packedglass tubes 22 is removed from the jig 11 and placed upon a stainlesssteel plate 26 having a silica-alumina (Fiberfrax) cloth 27 on its uppersurface, as shown in FIG. 4. Plate 26 is provided with a plurality ofperforations 28. Another silica-alumina cloth 29 is placed on the uppersurface of the assembly 25, and a second perforated stainless steelplate 30 is placed thereover. A heavy member 31 is finally placed on topof plate 30, and the entire assembly is then placed in a furnace andsubjected to heat sufficient to soften the glass walls of tubes 22 andcause the walls to bloat or expand due to the heating of the fluidmedium in each tube so that adjoining, contacting wall surfaces arefused together to form a unitary matrix.

It is important to have the ends of each of the tubes 22 in assembly 25sealed during the heating step, otherwise the tube walls will collapserather than expand when subjected to this heat. Furthermore, to utilizethe heating procedure described above with respect to the FIG. 4assembly, the length of the tubes should be no longer than the height ofthe rim 10. As the individual tubes expand, any air or other gases whichremains in the interstices passes through the perforations in the plates26 and 30. If desired, plates 26 and 30 need not be perforated, and theassembly can be placed under vacuum during the heating step to assist inthe removal of any air which is within the interstices between thetubes.

The heating of the thin-walled tubes expands them into close contactwith each other and into the interstices between tubes to a greater orlesser extent, ideally to an extent to substantially completely fill theinterstices between the tubes and between the tubes and walls of the rimand hub. In the latter event the resulting tubes become essentiallyhexagonal. The glass tubes are fusing together where they contact. Thetubes are fusing together and are also undergoing nucleation during theheat treatment, and heating of the structure is continued for a timesufficient to in situ crystallize the glass tubes to an at leastpartially crystalline material, commonly referred to as a glass-ceramic.

The rim and hub can be formed of a conventional inorganic crystallineoxide ceramic, made by firing and sintering particulate inorganic oxidematerials. The rim and hub should have an average coefficient of linealthermal expansion compatible with that of the low expansion material ofthe matrix. In a one embodiment of the invention, the rim and hub arealso formed of a thermally crystallizable glass which has beencrystallized to a glass-ceramic having physical properties, includingthermal expansion and contraction properties, which are close to, andusually the same as, those of the crystalline matrix comprising thefused tubes.

After the assembly 25 has been crystallized, and usually after coolingto room temperature, the outer surface portions of the assembly may beremoved by sawing with a diamond saw in the direction indicated by linesA in FIG. 4. An assembly of a predetermined thickness is thus obtained,and all of the fused tubes now have open channels since both sealed endsof each tube have been cut away.

In the method of this embodiment of the invention, the ends 22 of tubes22 are appropriately sealed, e.g., by means of a flame, either before,after, or during the bundling of the tubes. Typically, the tubes aresealed in a gaseous environment, so as to trap the environmental gaswithin each tube at the surrounding ambient pressure. On heating toeffect fusion sealing, the gas within each tube expands so as to preventcollapse of the tubes. With the thin-walled tubes used in thisinvention, expansion of the entrapped gas causes the tubes to bloat orexpand.

In a preferred embodiment the expansion is effected until the spacebetween adjacent tubes is essentially filled. When the tubes are bundledso that each tube is in contact with six adjacent tubes, as shown inFIG. 5, the tubes are reformed into substantially hexagonal shape toprovide the matrix structure illustrated in FIG. 6. The tube expansionmay be stopped short of full hexagonal development, but the wall-to-wallpressure created by even minimal expansion of the tubes has been foundeffective to form tube-to-tube seals which are sufficiently tenacious toknit the entire aggregate into an integral, unitary structure of goodmechanical properties. Conversely, open tubes without internal pressureacting upon each tube will collapse or deform under the influence ofgravity where high temperatures soften the glass enough to causetube-to-tube bonding.

Tubing used in practicing the usual embodiments of the method of thisinvention have maximum inner diameters of up to about 0.1 inch, wallthicknesses of 0.001 to 0.003 inch and inside diameter to wall thicknessratios of at least 6; substantially lower inside diameter to wallthickness ratios may result in a relative ineffectiveness of the processto urge the tubes into a good fusion bond when using a temperatureschedule which is also effective to properly nucleate and crystallizethe glass tubes to a glass-ceramic during the expanding and fusionheating cycle. In a now preferred embodiment of the invention the ratioof the inner diameter to the wall thickness of the thermallycrystallizable glass tubes is at least 7.2; when tubes having suchdiameter to wall thickness ratio are employed, the unique structure ofthe invention is made wherein the open frontal or cross sectional areaof the resulting matrix structure is at least 60 percent, and may be onthe order of 85 percent or more.

Usually, round thermally crystallizable glass tubing is used in formingthe matrix structure of the invention. Drawing of round glass tubing tocontrolled dimensions is an old, established art in industry.

While the assembled tubes 22 can merely be fusion sealed with slightexpansion and reformation of the tubes, it is preferred for mostapplications that the tubes be expanded and reformed into thesubstantially hexagonal shape during fusion sealing. Greater tube-totubepressure is generated causing a more perfect fusion of each tube to thesurrounding tubes and tube-totube contact area increases fromessentially tangential contact with adjacent tubes to essentially fullcontact, with bonding of the entire periphery of the tubes. Furthermore,as the triangular space between each set of three adjacent tubes (seeFIG. 5) is substantially reduced in area by expansion and reformation,the pressure drip in the finished product across the honeycomb structureis less than across one in which tubing is round in the final product.The thinner the wall thickness for a given composition and the greaterthe ratio of the inner diameter to such a wall thickness, the morereadily the tube can be expanded to a substantially hexagonal tube at agiven temperature.

In the application of Gray, a matrix of the type disclosed in the Peiapplication is reinforced by interposing a finely divided, thermallycrystallizable frit or other thermally crystallizable material betweenthe individual, sealed, matrix-defining glass tubes prior to the thermalconversion of the tubes to a glass ceramic. Subsequently, the thermallycrystallizable frit or other sinterable material and the individualtubes are jointly thermally processed through successive nucleating andcrystallizing steps to simultaneously convert both the tubes and thefrit to low expansion glass-ceramic materials having substantially thesame thermal expansion characteristics. During this joint thermalprocessing,

the internal pressures generated in theclosed tubes and the thermalsintering of the frit combine to compact and to integrate the tube-fritassembly into a single mass. After the nucleation and crystallizingsteps have been carried out, the ends of the tubes may be ground or cutoff to provide a flow-through matrix through the now opened ends of thetube. The frit is interposed between the ground or cut open ends of thetubes, and serves to reinforce the ends of the tubes and to provide anadditional, wear-resistant surface for the matrix assembly.

As shown in FIGS. 7 and 8, each of the glass tubes 22 is coated with asinterable frit to carry out the method of the Gray application. Thefrit l9 interposed in the interstices between the tubes is subjected tosubstantial pressures generated by the expansion of the tubing walls.The resultant sintering, melting, and distribution of the frit willadhere the tube walls to one another and to its own sinteredglass-ceramic mass. The open end face of a matrix is shown in FIG. 9which is formed from bundles of tubing shown in FIGS. 7 and 8. The tubewalls in FIG. 9 are therefore insured of support by another tube wall orby the sintered frit in the interstices.

While the matrix made according to the Gray application performs verywell, particularly where substantial radially directed load forces areinvolved, it is desirable to be able to reinforce the seal engagingsurface of a matrix by a method which requires less reinforcing materialand less time and labor in the assembling of the matrix to reduce thecost accordingly. Moreover, it is desirable in certain applications ofthe matrix to be able to control the porosity and the flow patternthrough the matrix.

Referring to FIGS. 10 and 11 there is shown top plan and sectionalviews, greatly enlarged, of a tube bundle portion from a matrixstructure taken from between lines A of FIG. 4. The matrix structure mayhave been subjected to a first or unified heat treatment process inwhich the assembly of FIG. 4 is taken from ambient to finalcrystallization temperature with no interruption in the process.Alternatively, the matrix may have been subjected to a second or twostep heat treatment process in which a first step bloats or expands andfusion bonds the tubes into a unitary or integral mass. The assembly isthen cooled somewhat or even cooled to room temperature and the ends ofthe tubes are ground or cut away and opened to atmospheric pressure. Theassembly is then heated again in a second step of the process into thefinal crystallization heat treatment range, where furthercrystallization is effected.

The matrix structure chosen for illustrating the teachings of thisinvention is one in which there has been sufficient bloating in the heattreatment process to expand adjacent tube walls into a fusion bondwitheach other, but the tubes have not been reformed into an essentiallyhexagonal shape. This structure enables an easier identification anddescription of interstices between tubes in the matrix. It is to beunderstood, however, that the teachings herein are also applicable to amatrix structure in which the tubes have been reformed to the hexagonalshape, leaving no interstices or very, very small interstices betweenthe tubes.

In FIGS. 10 and 11 the tubes 22 have been expanded to form an integralmass by the fusion bonding of tube wall portions 22a leaving interstices22b between the tubes 22. A paste or slurry 50 of low expansioncrystallizable frit carried in a liquid vehicle such as amyl acetatewith 1.2 percent nitrocellulose is mixed with a ratio of solids tovehicle which will advantageously keep the paste or slurry from flowingfreely.

The paste 50 is then applied to an open end face of the matrix betweenborder lines 51 and 52. An enlarged application area is shown in FIGS.10 and 11. FIGS. l2, 13, 14, 15 and 16 show diagrammatically alternativeopen network patterns of applications of paste 50 to the open end faceof a matrix. The choice of pinwheel, grid, radial spokes, concentriccircles, and spiral patterns, respectively, or a combination of patterns, is made dependent upon the characteristics of the seal bar whichwill engage the open end face of the matrix, the seal bar facingmaterial, rotation speed of the matrix, the pressure exerted by the sealbar on the matrix face, the matrix porosity desired, the desired flowpattern through the matrix, etc.

The area covered by the paste patterns may be defined by templates, bycontrol of the movement of a paste depositing mechanism, by use of asilk-screen type process, or simply by manually covering the areaoutside the paste pattern with a masking medium such as tape.

Depending upon the solids to vehicle ratio there will be some naturalflow of the paste 50 from the surface of the matrix into the open endsof the tubes 22 and into the interstices 22a (if any), as shown in FIG.11. If this penetration is insufficient, if the paste 50 is thick, or ifit is desired to insure that the top of the paste pattern is even withthe top of the tubes, then the paste may be mechanically urged into theopen tube ends and interstices by roller, brush, or the like mechanisms,or by hand.

After the solvent portion of the vehicle has evaporated and the binderportion of the vehicle has set up enough to give the paste patternsgreen-ware handling properties, the template or masking medium may beremoved (if used) and the matrix with the paste pattern thereon isplaced in a furnace.

The matrix and the paste pattern is then thermally processed to convertthe frit to a low expansion ceramic material which is fuse bonded to andis a part of the face of the matrix. The ceramic pattern areas thenprovide wear resistant surface areas, and a control of the porosity andflow through the matrix.

The paste patterns may be rolled or otherwise finished so that thepattern does not extend above the original open end surface of thematrix. Alternatively, the paste patterns may be left extending slightlyabove the surface. After firing, the ceramic pattern may be leftprojecting above the matrix surface to prevent seal bar contact with theoriginal matrix face, or the ceramic pattern may be surface ground downto the original surface level or to conform with the configuration of amating seal bar element.

The thermally crystallizable frit is preferably a finely divided ceramicmaterial (200 mesh in one example), which will have very low thermalexpansion characteristics after thermal processing. It is preferred thatthe final thermal expansion characteristics be substantially the same asthat of the matrix to which is applied. It is also preferred that boththe matrix and pattern materials be of a composition which can bethermally processed through successive nucleation and crystallizationstages to a low expansion glass ceramic. The matrix structure may be onewhich has already been processed to substantially completecrystallization before paste pattern application, or may be one whichhas been partially processed through nucleation and initialcrystallization. In the'latter case the matrix structure may be jointlyprocessed with the paste pattern to substantially completecrystallization.

Well suited for use in the method of this invention are thermallycrystallizable glasses that are convertible by heating to glass-ceramicbodies. As used herein, a glassceramic is an inorganic, essentiallycrystalline oxide ceramic material derived from an amorphous inorganicglass by in situ bulk thermal crystallization.

or more nucleating agents including TiO ZrO SnO or other knownnucleating agents. In general, such compositions containing in weightpercent about 64 to 79 SiO about 13 to 25 A1 and about 2 to 6 Li O,

together with about 1.2 to 4 weight percent of nucleating agentsselected from one or more of T ZrO and SnO can be employed. Preferably,not more than about 2.5 weight percent TiO is usually used or thecrystallization is undesirably rapid to be compatible with the fullestexpansion of the tubes in the bloating process.

Other ingredients can be present in small amounts, as is understood inthe art, such as even as much as 4 or 5 weight percent ZnO, up to asmuch as 3 or 4 weight percent CaO, up to as much as 8 percent MgO, andup to as much as 5 percent BaO, so long as the silica plus alumina pluslithia and the nucleating agent(s) are at least about 85, usually 90,weight percent of the total glass and the glass composition willthermally crystallize to a glass-ceramic having the desired lowexpansion of 18 t o 50 l0- /C. Exemplary compositions which can be usedin the process of the invention include those compositions disclosed inU.S. Pat. No. 3,380,818, those compositions disclosed in U.S. Ser. No.464,147 filed June 15, 1965, and corresponding British Patents 1,124,001 and 1,124,002, dated Dec. 9, 1968, and also those compositionsdisclosed in application Ser. No. 866,168 filed Oct. 13, 1969, andcorresponding Netherlands printed patent application 6,805,259.

As exemplary of suitable matrix tube compositions, the followingspecific formulations are presented:

TABLE I EXAMPLES OF SUITABLE MATRIX TUBE COMPOSITIONS INGREDIENT WEIGHTPERCENT I II III IV S10, 73.0 75.8 70.6 68.6 Al,0 17.65 16.8 19.7 21.34.15 4.44 3.7 4.0 ZnO 1.7 1.7 TiO 1.4 1.84 1.7 2.0 ZrO, 1.6 1.17 1.5 1.6Na,O 0.1 0.55 0.4 0.4 CI, 0.1 0.1 Sb,0, 0.3 0.5 0.3 K,O 0.2 0.2 F, 0.1MgO 0.1

As exemplary of suitable frit compositions which can be utilized, thefollowing compositions are presented:

TABLE II EXAMPLES OF SUITABLE FRIT COMPOSITIONS INGREDIENT WEIGHTPERCENT I II III S10; 56.1 75.8 73.0 A1 0 25.5 16.8 17.65 2 2.2 Fe O,0.03

10 "no, 0.14 1.84' 1.4 ZrO 2.67 1.17 1.6 Pb 0 0.50 Ca 0 0.01 Mg 0 0.02Zn 0 0.04 1.7 Na 0 0.9 0.55 0.1 x o 4.10 L 1 8.0 4.44 4.15 F, 0.13 01,0.1 sb o. 0.3

In any event, the thermally crystal-lizable glass tubings in thelithia-alumina-silica field containing nucleating agents as beforedescribed, are assembled as previously set forth and the constrainedbundles of scaled t'ubing(containing a heat exapnsible fluid) are heatedat any suitable rate that will not thermally shock the tubing up to atemperature range in the maximum nucleating range of the glass. Themaximum nucleation range can be determined for all such glasses by thegeneral method outlined in Smith U.S. Pat. No. 3,380,818 beginning atcolumn 9, line 43.

For the process of the present invention where sealing is to be effectedor initiated while nucleation is occurring, it is preferred that theassembled tubes be heated in the range 50 to 250 above the annealingpoint for a period of one hour or more. This time can be extended to 10or 20 hours, and even longer times are not harmful. During this time ofheating in such temperature range nucleation is effected, as well asfusion aided by pressure exerted by expansion of the entrapped fluid.Thereafter, the temperature is raised to a higher temperature than thefirst heating range, which higher temperature is at least 200F above theannealing point temperature or may be as high as the finalcrystallization temperature (usually 1,800 to 2,300F). The finalcrystallization can be effected at any such temperature range higherthan the nucleationexpansion-fusion temperature (50 to 250F above theannealing point temperature) and can be as low as 200F above theannealing point was high as 2,300F or as high as the upper liquidustemperature. If the final crystallization is effected at temperatures nomore than 400 or 500F above the annealing point, then the product willnot have .as high temperature stability as is desired forgas turbineuse, but the product will be of the desired low expansion glass-ceramic.

In any event, in this second stage of heating further expansion and thebeginning of crystallization is effected, followed by the completion ofcrystallization on continued heating to a degree such that the matrixmaterial has an expansion in the range from 18 to 50 -1-50 X 10- /C overthe range 0300C.

While the temperature may be raised directly to the finalcrystallization temperature at a furnace heating rate of at least 50Fper hour, it is usually preferred to allow crystallization to beeffected slowly while further expansion and concomitant fusion is beingeffected by having an intermediate step between the firstnucleation-and-fusion temperature range and the final crystallizationtemperature, which range is usually from 200F to about 500F above theannealing point of the original glass. Exemplary holding times in thisintermediate range are from 1 to 8 hours, after which the assembly isheated up to the final crystallization temperature, usually in the rangeof from about l,800 to 2,300F.

Obviously, no specific heat treatment instructions can be given suitablefor all thermally crystallizable glass compositions. As is well known,glass-ceramics do not have adequate strength if they are notsufficiently nucleated before crystals are allowed to grow appreciablyin size, so that routine experiments known to those skilled in the artare used to determine what length of time is best to obtain an adequatenumber of crystallization centers or nuclei in the glass in thenucleation temperature range of 50 to 250F above the annealing point.

Another point that must be kept in mind is that, if it is an object toobtain appreciable expansion beyond that necessary to get good fusionbetween the tubes, in other words to get appreciable reshaping of thetubes to fill the interstices between the tubing, one should not raisethe temperature too slowly when going from the nucleation temperaturerange to the intermediate range, since a rigid crystalline network maybegin to set in and to prevent further expansion. It is found somecompositions can be heated at a rate as low as 50F per hour to thisintermediate temperature range and still get sufficient expansion of thetubing effective to form the substantially hexagonal passages (roundtubes used in close-packed configuration). On the other hand, somecompositions have been found not to fully expand unless the heating ratefrom the initial nucleationfusion temperature range to the intermediatetemperature range is on the order of at least 200F per hour andpreferably at least 300F per hour.

The length of time of heating in the final crystallization temperaturerange of 1,800F to about 2,300F is from one-half hour to or 6 hours,although longer times are in no way deleterious. After thecrystallization has been completed, the structure can be cooled atfurnace rate or in air when the structure is of such low expansion thatthermal shock will not harm it.

When making a regenerator having a rim or having a rim and a hub, therim, as stated, can be made of a thermally crystallizable glass that isthe restraining means in which the tubes are initially packed, and therim can be heat treated concomitantly with the tubes which seal to therim during the process.

If, however, a rim of considerable thickness is desired and rapidheating rates such as 200 or 300 F per hour are used in the heattreatment of the matrix as just described, the glass of the rim maycrack from thermal shock. In such case it is possible to pre-heat treatthe rim to a partially crystallized state until it is a relatively lowexpansion material having an expansion coefficient less than to X l0 /C.This can be accomplished by using a suitable nucleation andcrystallization heat treatment where the top crystallization temperatureis on the order of 1,450 to 1,600F and the crystallization is effectedonly long enough to bring the coefficient of expansion down to thedesired range. This partially heat treated rim then can be used as therestraining means without fear of thermal shock. It is also possible touse a fully heat treated glass-ceramic rim or a fully formed and heattreated rim made of a low expansion sintered ceramic material known inthe art, such as ceramic materials that can be made, for instance, frompowdered petalite by suitable sintering methods known in the art. Thepaste pattern mixture may also be formed from such low expansionsinterable ceramic materials, if the thermal expansion characteristicsare compatible with those of the matrix. What has been said with respectto the rim also applies to regenerators having a hub of ceramic orglass-ceramic material.

After the heat treatment just described, the product may now be cooledand the sealed ends of the tubes cut or ground away to open each tube toatmospheric pressure. Alternatively, if the intermediate step of heattreating is employed, the heat treatment can be interrupted after thisintermediate step and cooled somewhat or even cooled to roomtemperature, and the ends of the tubes cut or ground away and opened toatmospheric pressure. Then the assembly can be heated up again into thefinal crystallization heat treatment range, where furthercrystallization is effected. As noted hereinbefore the paste patternsmay be applied to this intermediate matrix form and the matrix and pastejointly thermally processed into a desired crystallization state. Aswill be understood by those skilled in the art, the crystals of thematrix after this second stage of heat treatment may be in thebeta-eucryptite or betaeucriptite-like state, as is referred to in thereferenced Smith U.S. Pat. No. 3,380,818, and already be highlycrystallized and of a low expansion. The final heat treatment will causefurther crystallization and conversion of the eucryptite-like crystalsto beta-spodumene or beta-spodumene-like crystals, as is also describedin the cited Smith patent. The following examples will serve toillustrate the invention without in any way limiting it, sincemodifications will be readily apparent to those having ordinary skill inthe art.

EXAMPLE I Glass tubing formed from composition III of Table I having anaverage outside diameter of 0.030 inch, average inside diameter of 0.026inch, and an average wall thickness of 0.002 inch and having an averagelength of 3.5 inches, the tubing having closed ends, are closely packedinto a mold similar to that illustrated in FIG. 1.

- The tubing and ring mold are then combined into the assembly 25 ofFIG. 4 and thermally processed in a furnace according to the schedule inExample III of the Pei application. The ends of the resulting matrix areground open with a diamond abrasive wheel exposing an open end facesimilar to that illustrated in FIG. 10. A paste or slurry is mixedcontaining a powdered mixture of composition I of Table II of about 200mesh fineness in a vehicle consisting of Amyl acetate with 1.2 percentnitrocellulose, in a ratio of 3.5:1 to 2:1 (by weight) solids to vehicleto prevent the paste from flowing too freely.

The paste-frit is then applied to the open face of the matrix in thegrid pattern of FIG. 13, in strips about 0.25 inch wide. The matrix andpaste-frit pattern are then heat treated in a furnace on the followingschedule.

Temperature Time or Rate Ambient to 2000F F/Hr. Hold at 2000F 2 to 4hrs. 2000F to I800F 50F/I-Ir. l800"F to Ambient 200F/Hr.

After this second heat treatment, the resulting glassceramic matrix maybe used as a regenerator in one of the structural forms detailed in thePei application. The foregoing first heat treatment thermally in situcrystallized the tubing and produced a glass-ceramic matrix. The secondheat treatment fusion bonded with pastefrit to and just below thesurface of the matrix in the open ends of tubes and interstices coveredby the pattern. The normal open frontal area is reduced about 5 percentby the pattern and a wear-resistant reinforced surface is provided forcontact with a seal bar to prevent fracturing or other destruction ofthe open ends of tubes not covered by the pattern. The reinforcedsurface has been thermally converted to a very low expansion glaze orceramic which has thermal expansion characteristics compatible with theexpansion characteristics of the matrix.

This example illustrates that a wear-resistant, porosity-controllingreinforcing surface may be provided for a matrix which has already beenthermally processed to substantially complete crystallication beforeapplication of a paste-frit pattern to form the wear-resistant surface.The powdered low expansion crystallizable frit may consist of a mixtureof two different compositions from Table II which have differentcoefficients of lineal thermal expansion to obtain a mixture having anoverall coefficient of lineal thermal expansion which substantiallymatches the still different coefficient of lineal expansion of thetubing which is formed from composition III of Table I, when all havebeen thermally crystallized into the glass-ceramic matrix. Moreover,mixtures of different frit compositions may be used to obtain desirableor matching chemical characteristics.

EXAMPLE II Glass tubing formed from composition I of Table I having anaverage outside diameter of 0.030 inch, average inside diameter of 0.026inch, and an average wall thickness of 0.002 inch and having an averagelength of 3.5 inches, the tubing having closed ends, are closely packedinto a mold similar to that illustrated in FIG. 1. The mold and tubesare then combined into the assembly 25 of FIG. 4 and heated in a furnacefor the first step of the heat treatment process on the followingschedule:

Temperature Time or Rate Ambient to 900F 100F per Hr. Hold at 900F 2hours 900F to 1300F 100F per Hr. 1300F to 1375F 100F per Hr. Hold atI375F 24 hours l375F to 1725F 10F per Hr. Hold at 1725F 24 Hours 1725Fto l800F 5F per Hr. Hold at 1800F 6 Hours 1800F to 1500F 50F per I-Ir.lSF to Ambient 150per Hr.

The tube ends are then cut off with a saw to expose an open end face ofthe matrix. A paste or slurry is mixed containing a finely divided fritof about 200 mesh consisting of composition III of Table II in a vehicleof amyl acetate with 1.2 percent nitrocellulose, in a ratio of 3.5:1 to2:1 (by weight) solids to vehicle, again of a consistency to prevent thepaste from flowing freely. The paste-frit is then applied to the openface of the matrix in the pinwheel pattern of FIG. 12, the patternstrips being about 0.25 inch wide.

A second step heat treatment schedule for the combined matrix and pastepattern assembly is as follows:

Temperature Time or Rate Ambient to I800F 100F per Hr. I800F to 2100F50F per Hr. Hold at 2100F 6 hours 2100? to 1700F 50F per Hr. 1700F toAmbient 300F per Hr.

ity controlling reinforcing surfaces and having the same structural andlow expansion characteristics as those described for the matrix ofEXAMPLE I.

This example is provided to illustrate that it is fre- 5 quentlydesirable to use a frit composition for the paste which is the same asthe composition of the glass tubing to obtain substantially the samecoefficient of lineal expansion along the open ends of the tubing at thepattern on the face of the glass-ceramic matrix. This example furtherillustrates that a two step heat treatment may be used in which aconstrained bundle of sealed tubing is first heated to expand or bloatthe tubes for initial fusion and to heat the tubes to a temperaturerange in the maximum nucleation range. The first step induces a glassysintering of the material, wherein the material is not fullycrystallized, is partially transparent, and is in a high quartz form.The second step or final heat treatment converts the tubing into fullopacity or substantially full crystallization as a glass-ceramic matrixand converts the paste-frit pattern into a glass-ceramic reinforcingsurface that is fusion bonded to the matrix. This two step process isuseful for materials that cannot stand the mechanical and chemicalstrains of the one step or unified heat treatment cycle described in EX-AMPLE I.

The vehicle usedfor the slurrys in EXAMPLES I and II is exemplary onlyand was chosen for the characteristics of a good initial drying speedprovided by the amyl acetate solvent for the nitrocellulose, and for theability of the nitrocellulose to bind the frit particles together toprovide good green-ware handling properties.

It should further be noted that ordinary sinterable ceramic powdershaving a very low expansion may be useful for certain pasteapplications. These powders will sinter or adhere together and to theopen ends of the tubes and interstices creating a fusion chemical bondbetween particles and the tubes. While there is normally a reduction insize of these powdered particles when sintered, they can be used in thematrix formation herein by providing a paste strip build-up above theface of the matrix and then grinding the converted ceramic to facelevel, as long as the resultant thermal expansion and chemicalcharacteristics are compatible with the tubing in the matrix.

For many applications, particularly when the matrix is used as a heatexchanger, a low expansion and heat/- thermal shock resistant matrix isrequired. For instance, when used as a regenerator in a gas turbine, hotgas from the turbine can be passed through a rotating open-ended matrixin one direction, while cold incoming air is passed through the matrixin the opposite direction, picking up heat from the matrix passageways.

Therefore, a preferred embodiment of this invention utilizes thermallycrystallizable glass compositions for the tubes which in theircrystallized state,

1. have essentially zero porosity,

- 2. consist essentially of an inrganic crystalline oxide ceramicmaterial,

3. have an average coefficient of lineal thermal expansion of about 12to +12 10 /C in a range 0300C, and preferably a coefficient of about -5to +5 X 10 /C in a range 0300C, and

4. a thermal conductivity of less than 0.01 cal/cm- /sec/cm/C at 400C.

When the matrix tubes have such a coefficient of expansion it ispreferred, also,that the expansion coefficient of the paste-fritmaterial also be in the 12 to +12 (preferably to +5) X l0"/C range overthe temperature range 0300C.

As used herein the term glass-ceramic is an inorganic crystalline oxideceramic material containing a multiplicity of extremely small inorganicoxide crystals in random orientation throughout the mass of thematerial, which glass-ceramic is formed by the thermal in situ bulkcrystallization of a glass.

Also as used herein the term inner diameter refers to the shortestdistance through the center of the tube or passageway from one innerwall to the opposite inner wall. This distance is the same for alldiameters of a circle, of course, but for a hexagon, for instance, thediameter defined herein is the distance of a line through the center ofa hexagon and perpendicular to the opposite side walls of the hexagon.

It should be noted that both open-ended faces of a matrix may besimilarly reinforced by the method described herein. The reinforcingsurfaces for the opposing faces may be thermally processedsimultaneously or at different times. It should also be noted that whileit may be desirable for some aplications that the tube ends andinterstices (if any) adjacent the pattern be completely filled with thereinforcing material after the thermal treatment is completed, thestructure is functional if the tube ends and/or interstices are notfilled, as long as a surface is present which will provide the desiredwear-resistance and reinforcement.

While there have been shown and described and pointed out thefundamental novel features of theinvention with a reference to thepreferred embodiments thereof, those skilled in the art will recognizethat various changes, substitutions, omissions and modifications in themethods and structures described may be made by those skilled in the artwithout departing from the spirit of the invention.

I claim:

1. A regenerator matrix comprising a. a plurality of open-ended tightlypacked axially elongated tubes formed of ceramic material arranged withtheir axes substantially parallel and having adjacent tube walls joinedtogether to form an integral mass having a series of longitudinalparallel passageways formed therethrough, and

b. an open network pattern of sintered ceramic material on an open-endedface of said integral mass fusion bonded to open tube ends adjacent saidpattern to provide a wear-resistant, reinforcing surface for said openend of said mass,

0. said tubes and said sintered ceramic pattern having substantially thesame thermal expansion characteristics.

2. A regenerator matrix as defined in claim 1 wherein the tube walls a.consist essentially of an inorganic crystalline oxide ceramic material,and

b. have an average coefficient of lineal thermal expansion of about '1 8to +50 X l0/C in the range 0-300C.

3. A regenerator as defined in claim 2 in which the sintered ceramicsurface material a. consists essentially of an inorganic crystallineoxide ceramic material, and

b. has an average coefficient of lineal thermal expansion of about l8 to+50 X l0 /C in the range 0-300C.

4. A regenerator matrix as defined in claim 3 in which the tube wallsand the sintered ceramic surface material have an average coefficient oflineal thermal expansion of about l2 to +12 X lO /C in the range 0300C.

5. A regenerator matrix as defined in claim 3 in which the tube wallsand the sintered ceramic surface material have an average coefficient oflineal thermal expansion of about 5 to +5 X l0 /C in the range 0300C.

6. A regenerator matrix as defined in claim 1 in which the tube wallshave essentially zero porosity.

7. A regenerator matrix as defined in claim 1 in which the tube wallshave a thermal conductivity of less than 0.01 cal/cm/sec/cm C.

8. A regenerator matrix as defined in claim 1 in which each tube has aratio of inner diameter to wall thickness of at least 6.

9. A regenerator matrix as defined in claim 1 in which each tube has aratio of inner diameter to wall thickness of at least 7.2.

mg UNITED STATES PATTENT OFFICE CERTIFICATE OF CORRECTION Patent3,771,592 Dated November 13, l973 Inventofls) JAMES A SAYERS It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below":

r column 9, line 65, delete "SiO and substitute Column 1d, line 51-,change "50+50 x l0 /C" to n +50 x 1o' /c Column 12, line 63, delete"with and substitute Column 14, line 57, delete "inrganic" andsubstitute inorganic Column 16, line 16, (first line of claim 3)v after"regenerator" insert matrix and sealed this 23rd day of April 197M;

( All fattest:

i-LDX'JARIE iiOFLLiTCEirIF'i Ji'is, C. MAZKSl-IALL DARN I F! n ant ulLl)iflcer Commissioner of Patents

1. A regenerator matrix comprising a. a plurality of open-ended tightlypacked axially elongated tubes formed of ceramic material arranged withtheir axes substantially parallel and having adjacent tube walls joinedtogether to form an integral mass having a series of longitudinalparallel passageways formed therethrough, and b. an open network patternof sintered ceramic material on an open-ended face of said integral massfusion bonded to open tube ends adjacent said pattern to provide awear-resistant, reinforcing surface for said open end of said mass, c.said tubes and said sintered ceramic pattern having substantially thesame thermal expansion characteristics.
 2. A regenerator matrix asdefined in claim 1 wherein the tube walls a. consist essentially of aninorganic crystalline oxide ceramic material, and b. have an averagecoefficient of lineal thermal expansion of about -18 to +50 X 10 7/*C inthe range 0*-300*C.
 3. A regenerator as defined in claim 2 in which thesintered ceramic surface material a. consists essentially of aninorganic crystalline oxide ceramic material, and b. has an averagecoefficient of lineal thermal expansion of about -18 to +50 X 10 7/*C inthe range 0*-300*C.
 4. A regenerator matrix as defined in claim 3 inwhich the tube walls and the sintered ceramic surface material have anaverage coefficient of lineal thermal expansion of about -12 to +12 X 107/*C in the range 0*-300*C.
 5. A regenerator matrix as defined in claim3 in which the tube walls and the sintered ceramic surface material havean average coefficient of lineal thermal expansion of about -5 to +5 X10 7/*C in the range 0*-300*C.
 6. A regenerator matrix as defined inclaim 1 in which the tube walls have essentially zero porosity.
 7. Aregenerator matriX as defined in claim 1 in which the tube walls have athermal conductivity of less than 0.01 cal/cm/sec/cm2*C.
 8. Aregenerator matrix as defined in claim 1 in which each tube has a ratioof inner diameter to wall thickness of at least
 6. 9. A regeneratormatrix as defined in claim 1 in which each tube has a ratio of innerdiameter to wall thickness of at least 7.2.